By Alison Roberts
BBC News, in Portugal
The McCanns could be interviewed by UK police
Police papers from the inquiry into the disappearance of Madeleine McCann are due to be passed to the public prosecutor in Portugal. But what are his options?
With Kate and Gerry McCann back home in the UK, the Portuguese authorities are weighing up what action to take next in relation to them and Robert Murat - the other formal suspect in the investigation into the disappearance of the McCanns' four-year-old daughter Madeleine.
Detectives in Portimao have been preparing the case files to hand them over to Jose Cunha de Magalhaes e Meneses, the prosecutor overseeing their work, for him to review progress and redirect the investigation if necessary.
"The public prosecutor wants to see the case files," said Chief Inspector Olegario de Sousa, the police spokesman for the investigation.
"Normally we keep him up to date verbally, but when he wants to look at them, we hand them over."
Police said they expected to hand over the files on Tuesday. Once they have done so, the prosecutor will draw together the evidence they contain and decide the next step.
He could conclude there is enough evidence to draw up a charge sheet against one or more of the arguidos, or formal suspects, in the case - Robert Murat and Kate and Gerry McCann - thus bringing the investigation to a close, or that one or more of them should have that status removed, for lack of evidence.
More likely is he will direct police to gather more evidence - for example by carrying out further searches or witness interviews - and to cross-check this with existing information.
If police want to interrogate Kate or Gerry McCann further, then they must formally notify them of that fact.
Mr and Mrs McCann would then have five working days from when they, or their Portuguese lawyer, receives the letter before having to appear.
If the McCanns refused to return for questioning, the Portuguese could formally request that UK police interrogate them instead, putting to them a list of questions sent from Portimao, perhaps with a Portuguese detective observing.
But all this would mean more bureaucracy, slowing down proceedings.
"As soon as suspects leave the country, another jurisdiction enters the picture," said Rogerio Alves, the head of Portugal's Order of Lawyers.
Robert Murat is the only other formal suspect
"All formal requests will have to be scrutinised by the court system there unless they come voluntarily."
In any case, now the McCanns are arguidos, they are no longer obliged to answer questions during interrogation.
So from the point of view of police, obtaining further evidence becomes still more crucial.
That evidence could come in the form of further results from DNA and other tests done on samples sent some six weeks ago to a forensic laboratory in Birmingham.
These were taken at the apartment from which Madeleine disappeared on 3 May and from a car used by the McCanns more than three weeks afterwards, as well as from other vehicles and sites deemed relevant to the investigation.
It was what police described as "partial results" from those tests which seem to have triggered last week's questioning of the McCanns, during which they became arguidos.
Police say they do not know when the full results will be in, while the Birmingham laboratory said that tests on the samples would continue.
Police could force Kate or Gerry McCann to return to Portugal by issuing arrest warrants, which under European Union accords should be executed by the British authorities within 40 days.
Such a move would, however, be worthwhile only if police had sufficient evidence of a serious enough crime to convince a Portuguese judge they should be held in some form of custody.
As to how long the McCanns could remain formal suspects without being charged, in principle it is for eight months.
That could be extended by four months, for example on grounds that the need to shuttle correspondence between Portugal and the UK results in delays.
Once the first eight months are up, one of two things could happen: an arguido may formally request that the investigation be accelerated. This move is, however, in itself not binding.
"The deadlines are recommended only," said Portuguese lawyer Nelson Lourenco. "If they're not kept to, there's no real comeback."
Alternatively, Portugal's attorney general could step in, on the grounds that one or another deadline for the investigation has been exceeded, and take charge of the case.
In fact, he can intervene earlier if he takes the view that police were treating an individual as a suspect before formally declaring them an arguido.
In any case, police have indicated the McCanns are unlikely to remain in their current situation for more than eight months without being charged or cleared, given that the prosecutor has asked for the case files so soon after they were declared arguidos.
Chief Insp de Sousa said: "The investigation could take several more months. It could be up to one year. But in this case that's unlikely, since the prosecutor is analysing the files now. It shouldn't take long."
Police, he added, will continue their efforts to discover what happened on 3 May, even as the prosecutor pores over the case files.
"In an investigation of this kind there are always things to do," he said.